Guide wires are generally elongate structures for use in medical procedures. During such procedures, a distal portion of the wire is positioned within a lumen of a patient's body to acquire and/or maintain access to a region of interest. For example, such a region of interest of a patient's body may include a locally stenosed lumen at a location in the patient's vascular system. A catheter can be advanced over a guide wire for treatment or diagnostic purposes.
The guide wire and catheter are positioned within the patient's body by an operator such as a medical doctor. A proximal portion of the wire and a proximal portion of the catheter extend outwardly from the patient's body for manipulation by the operator. The operator steers the guide wire to a treatment site by forming a small bend on the distal end of the wire, introducing the wire percutaneously into the patient's body, and advancing and torqueing the guide wire until the region of interest is reached. The guide wire can be directed into an off-axis channel by torqueing the wire until the bent tip enters the channel and then advancing the guide wire further into the channel. In the case of over-the-wire systems, at least a portion of the wire must extend proximally relative to the proximal end of the catheter, thereby allowing the catheter to be manipulated axially relative to the wire.
Guide wires may be maintained at an intended axial position within the lumen of the patient's body so as to afford access to a treatment or diagnostic site. The wire may be maintained by any means that enable the relative position of the wire to be established within the lumen, such as by an anchored distal protection device, or by manually maintaining the position of the wire within the lumen. Once an axial position is established, the wire is maintained in position to allow devices such as a balloon catheter, a stent, a distal protection device, an atherectomy catheter, a thrombectomy catheter, or the like to be advanced over the wire to the treatment or diagnostic site.
Guide wires have several key performance requirements. Flexibility is needed for adequate tracking in tortuous anatomy. Flexibility and control of movement is particularly desirable at the distal end of a guide wire. The guide wire preferably has isotropic bending characteristics along the proximal shaft region to prevent occurrence of whipping during application of torque. In addition, the guide wire needs good structural integrity so that it does not bend undesirably, kink, or pull apart in tension. Guide wires need to have good torsional stiffness along their entire length so they can be steered into a region of interest by application of torque. At least a portion of a guide wire needs to be radiopaque so that it can be viewed fluoroscopically during an interventional procedure.
Guide wires often include a “floppy tip” at their distal end. The floppy distal tip provides an atraumatic and radiopaque terminus and can be any desired length. An atraumatic tip prevents vessel injury during initial placement or subsequent advancement of the guide wire. A radiopaque tip helps the physician verify suitable tip placement during fluoroscopy. The floppy tip can comprise a springy or resilient material, such as a metal (e.g., stainless steel, iron alloys such as Elgiloy™, and shape memory metal such as nitinol) or polymer (e.g., polyetheretherketone (PEEK), polyimide, polyester, PEBAX, urethane, polytetrafluoroethylene (PTFE), and the like). Springy materials are desirable because they tend to retain their shape. The physician will initially shape the tip, typically with a slight curve, and then as the wire is advanced through the body the tip will be deflected as it encounters obstacles. It is desirable, after the inevitable deflections during insertion, that the tip restores itself to the pre-set shape.
The transition between a guide wire and its distal tip is most preferably smooth and continuous to promote pushability and tracking. State of the art guide wires employ various distal tips which include radiopaque coils and sheaths. Frequently, coil tips are bonded or welded to the distal end of the guide wire, resulting in stiffened areas that affect the flexibility and handleability of the guide wire. An added disadvantage is that coils require an attachment method such as welding, soldering, or adhesive bonding, which can adversely affect fluoroscopic tracking. Radiopaque sheathed tips can also result in undesirable stiffness at the distal end of a guide wire. Further, conventional coiled guide wire tips are not strong in tension and it is not unusual for a guide wire tip to separate from the guide wire during use. Tip separation is often accompanied by lengthening and unwinding of the coil which offers minimal resistance to tensile forces due to the fact that the coil turns are substantially transverse to the coil axis. Although safety wires are often added to guide wire tips to prevent coil lengthening, such wires must be small in cross section to prevent adding unwanted stiffness to the tip of the guide wire. Because their cross-sectional area must be low, the strength of safety wires is limited.
Still needed in the art are guide wires that are particularly easy to advance and control and are flexible for their entire length yet which are sufficiently strong in tension to prevent damage during use. In particular, a more flexible and torquable distal end of the guide wire would be desirable.